Make poll_for_updates Send

[skairunner]

Describe the feature request

Currently poll_for_updates is !Send. It would be nice if it could be made Send.

Background

Because poll_for_updates is !Send, it can't be spawned using tokio::spawn or other similar methods and must be on either an actual thread or a local task set. This is not super ergonomic: a common pattern in async applications seems to be spawning persistent tasks like poll_for_updates with tokio::spawn in a 'fire and forget' manner.

Solution suggestions

I haven't looked at the code yet to see if making the function Send is an easy or hard task.

[skairunner]

I am trying to reproduce this issue in the test suite.

spawn(async { client.poll_for_updates().await; });

The above code fails with this error in the project I'm using:

error: generator cannot be sent between threads safely
   --> 87:5
    |
87  |     tokio::spawn(async {
    |     ^^^^^^^^^^^^ future created by async block is not `Send`
    |
    = help: the trait `std::marker::Send` is not implemented for `dyn StdError`
note: required by a bound in `tokio::spawn`
   --> /Users/sky/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.18.2/src/task/spawn.rs:127:21
    |
127 |         T: Future + Send + 'static,
    |                     ^^^^ required by this bound in `tokio::spawn`

I can't reproduce the error with similar code in the test suite, so further investigation is required.

[skairunner]

It seems that the issue is currently fixed on the master branch, while I'm using 0.6.